Alumina Refractory
The alumina-silica (SiO2) group of refractories includes alumina (Al2O3) refractories, which correspond to the SiO2 -Al2O3 phase equilibrium system. They differ from fire clay refractories in terms of Al2O3 content, with Al2O3 levels typically exceeding 45 percent. These refractories have a different raw material base than fire clay bricks.
Because of their outstanding slag resistance and mechanical qualities, alumina-magnesia and alumina-spinel castables have been broadly applied in steel ladle linings below the slag zone, the well block of purging plugs, and injection lances. Because of the rising scrap-to-steel ratio, greater working temperatures, and longer refining times, materials with improved characteristics, particularly slag resistance and thermal shock resistance, are needed to adapt to harsher service conditions. Slag penetration is generally reduced by employing thick aggregates and loading the matrix with fine powders to make it less porous.
Nonetheless, under a high temperature difference, dense aggregates and matrices find it difficult to discharge thermal stress. In terms of actual applications, it is vital to simultaneously optimize slag resistance and thermal shock resistance. The use of innovative porous aggregates has recently succeeded in breaking the standard idea, and it has become a hot topic in refractories. In recent years, extensive research on porous aggregates has been conducted. The apparent porosity of aggregates increased from 4.2 percent to 42 percent, marginally enhancing the flexural strength of corundum-spinel castables. A improved interface bonding between both the matrix and porous cordierite aggregates was established in lightweight cordierite-mullite refractories, resulting in good strength and thermal shock resistance. The introduction of porous aggregates significantly restricted the penetration of slag towards matrices, according to Yan et al.
Furthermore, porous aggregates can significantly lower material thermal conductivity, increasing the energy efficiency of high-temperature vessels. However, as previously said, porous aggregates have significant advantages over conventional aggregates. Lightweight corundum and periclase-spinel aggregates are the terms used to describe the lightweight aggregates used in steel ladles today.
Although, the development of new multicomponent lightweight aggregates, such as CMA (CaOMgO-Al2O3) aggregates primarily composed of spinel, CA (CaAl2O4), and CA2 (CaAl2O4), gave an alternative for the design and use of refractories (CaAl4O7). As a result of the in situ creation of a protective layer on the surface of the bricks, the slag resistance of magnesia-carbon (MgO-C) bricks for steel ladle linings was greatly increased with CMA aggregates addition. Wöhrmeyer et al. exhibited the corrosion mechanism of alumina spinel castables with the addition of CMA aggregates. According to the findings, a thin densified zone emerged, which prevented slag penetration into the porous matrix and porous aggregates.
Castables’ all-around performance, on the other hand, was crucial for the applications. Because aggregates can have a significant impact on numerous areas of castable performance, CMA aggregates of varied particle sizes were chosen for this study. The effect on characteristics of alumina-spinel castables, particularly slag resistance and thermal shock resistance, was examined. The goal of this study was to use CMA aggregates to improve the characteristics of alumina-spinel refractory castables.
All castables were cured for 48 hours at 20 °C and 70–75 percent relative humidity after casting, then dried for 24 hours at 110 °C. All samples were calcined for 3 hours at 1100°C and 1550°C, respectively. The Archimedes approach was used to determine the apparent porosity and bulk density of materials using the GB/T 2997–2000 standard [17]. Three-point bending tests were used to determine the cold modulus of rupture (CMOR) in accordance with GB/T 3001–2007 [18]. X-ray diffraction (XRD, X’pert Pro MPD, Philips, Almelo, The Netherlands) was used to determine the phase composition of castables. Scanning electron microscopy was used to examine the microstructure of the specimens (SEM, JEOL JSM-6610, JEOL Ltd., Tokyo, Japan).
The samples were tested for slag resistance using the static crucible method as described in GB/T 8931–2007 [19]. Table 3 shows the chemical makeup of slag. Samples were sliced open along the center line after being heated at 1550 °C for 3 hours to observe the state of corrosion. The corrosion and penetration indexes were determined using the equations Ic = Acl/Ac 100 percent and Ip = Apl/Ac 100 percent, where Acl is the slag-corroded area, Apl is the slag-penetrated area, and Ac is the crucible area. According to YB/T 2206.1–1998 [20], the thermal shock resistance was tested using the air quenching method (5 cycles). Three aggregates with different microstructures: (a) white fused alumina, (b) tabular alumina, and © CMA aggregates. After casting, all castables were cured for 48 hours at 20°C and 70–75% relative humidity before being dried at 110°C for 24 hours. All samples were calcined for 3 hours at 1100°C and 1550°C, respectively.
The Archimedes approach was used to determine the apparent porosity and bulk density of materials using the GB/T 2997–2000 standard. Three-point bending tests were used to determine the cold modulus of rupture (CMOR) in accordance with GB/T 3001–2007 [18]. X-ray diffraction (XRD, X’pert Pro MPD, Philips, Almelo, The Netherlands) was used to determine the phase composition of castables. Scanning electron microscopy was used to examine the microstructure of the specimens (SEM, JEOL JSM-6610, JEOL Ltd., Tokyo, Japan). The static crucible method was used to test the samples for slag resistance according to GB/T 8931–2007. After 3 hours of heating at 1550°C, samples were sliced open along the center line to check for corrosion.
The corrosion and penetration indexes were determined using the equations Ic = Acl/Ac 100 percent and Ip = Apl/Ac 100 percent, where Acl is the slag-corroded area, Apl is the slag-penetrated area, and Ac is the crucible area. According to YB/T 2206.1–1998, the thermal shock resistance was evaluated using the air quenching method (5 cycles). The samples were first heated to 1100°C in an electric furnace for 30 minutes before being cooled to room temperature with compressed air.
Elastic Modulus & Damping System was used to test the elastic modulus of samples after each heat cycle (RFDA, HTVP1600, IMCE, Genk, Belgium). Furthermore, the specimens’ residual strength and elastic modulus after all castables were treated for 48 hours at 20 °C and 70–75 percent relative humidity after casting, then dried for 24 hours at 110 °C. All samples were calcined for 3 hours at 1100°C and 1550°C, accordingly. The Archimedes approach was used to determine the apparent porosity and bulk density of materials using the GB/T 2997–2000 standard. Three-point bending tests were used to determine the cold modulus of rupture (CMOR) in accordance with GB/T 3001–2007 [18]. X-ray diffraction (XRD, X’pert Pro MPD, Philips, Almelo, The Netherlands) was used to determine the phase composition of castables.
Scanning electron microscopy was used to examine the microstructure of the specimens (SEM, JEOL JSM-6610, JEOL Ltd., Tokyo, Japan). The samples’ slag resistance was tested using the static crucible method, as described in GB/T 8931–2007. Samples were sliced open along the center line after being heated at 1550 °C for 3 hours to observe the state of corrosion. The corrosion and penetration indexes were determined using the equations Ic = Acl/Ac 100 percent and Ip = Apl/Ac 100 percent, where Acl is the slag-corroded area, Apl is the slag-penetrated area, and Ac is the crucible area. According to YB/T 2206.1–1998, the thermal shock resistance was evaluated using the air quenching method (5 cycles). Three aggregates with different microstructures: (a) white fused alumina, (b) tabular alumina, and © CMA aggregates. After casting, all castables were cured for 48 hours at 20°C and 70–75% relative humidity before being dried at 110°C for 24 hours. All samples were calcined for 3 hours at 1100°C and 1550°C, accordingly. The Archimedes approach was used to determine the apparent porosity and bulk density of materials using the GB/T 2997–2000 standard. Three-point bending tests were used to determine the cold modulus of rupture (CMOR) in accordance with GB/T 3001–2007. X-ray diffraction (XRD, X’pert Pro MPD, Philips, Almelo, The Netherlands) was used to determine the phase composition of castables. Scanning electron microscopy was used to examine the microstructure of the specimens (SEM, JEOL JSM-6610, JEOL Ltd., Tokyo, Japan).
The samples’ slag resistance was tested using the static crucible method, as described in GB/T 8931–2007. Table 3 shows the chemical makeup of slag. After 3 hours of heating at 1550°C, samples were sliced open along the center line to check for corrosion. The corrosion and penetration indexes were determined using the equations Ic = Acl/Ac 100 percent and Ip = Apl/Ac 100 percent, where Acl is the slag-corroded area, Apl is the slag-penetrated area, and Ac is the crucible area. According to YB/T 2206.1–1998, the thermal shock resistance was evaluated using the air quenching method (5 cycles). The samples were first heated to 1100°C in an electric furnace for 30 minutes before being cooled to room temperature with compressed air. Elastic Modulus & Damping System was used to test the elastic modulus of samples after each heat cycle (RFDA, HTVP1600, IMCE, Genk, Belgium). Furthermore, the samples’ residual rigidity and elastic modulus.
Bauxite was discovered in 1822 at the village of “Les Baux de Provence” in France by a scientist called Berthier, who identified an ore that was rich in alumina but low in iron. Because it is predominantly made up of aluminum hydroxides, it is commonly referred to as aluminum ore. The eventual use for bauxite, as well as the technique required to create it, is determined by the quality of the ore and the kind and amount of aluminum and other minor minerals present. About 95 percent of the world’s bauxites are used in the aluminum market, which is primarily focused on metallurgical applications. Bauxites for the manufacturing of high-alumina refractories are found in isolated deposits. Refractories with alumina (Al2O3) content of 47.5 percent or greater are referred to as high-alumina refractories. This descriptive designation separates them from other alum inosilicates with an alumina content less than 47.5 percent, which are mostly formed of clay or other alum inosilicates.
Refractories
A short summary: By definition, refractory materials are heat resistant and are subjected to varying degrees of mechanical and thermal stress and strain, as well as corrosion/erosion from solids, liquids, and gases, gas diffusion, and mechanical abrasion at varying temperatures. Molded (bricks and cast shapes) and unshaped (monolithic) refractories are the two basic kinds. Various refractories are created and manufactured with distinct qualities ideal for certain purposes in these conditions. The raw materials for making the refractory goods, as well as the methods utilized to manufacture the refractory products, determine the characteristics of each refractory category. Most refractory materials come in preformed shapes, however monolithic refractories have evolved and increased greatly in the last 40 years, becoming the refractories of choice in many applications due to improved performance and ease of installation.
Furthermore, in leading countries, the fraction of unshaped refractories in the overall balance has reached 50% to 60%. Refractory castables, which are premixed compositions of refractory aggregates, matrix components, bonding agents, and admixtures, stand out in this category. The castable is mixed with a liquid (usually water) and vibrated, poured, pumped, or pneumatically shot into position at the point of installation to form a refractory shape or structure that becomes stiff due to hydraulic or chemical setup. The refractory aggregates constitute the castable’s skeleton, accounting for the majority of the formulation and being proportioned to provide the correct packing and particle size distribution. A wide range of aggregates are available, and castable formulations can be based on only one type or a mixture of them, depending on the desired qualities. In this environment, high alumina materials account for 70% of global output, and refractory grade bauxite is frequently used as the primary raw material.
